1. Field of the Invention
The present invention relates to an ink-jet recording method which is suitable for the formation of images using inks containing a pigment component, and a print obtained by the ink-jet recording method.
2. Related Background Art
An ink-jet recording system is a recording system in which minute droplets of an ink are ejected by any of various working principles to apply them to a recording medium such as paper, thereby making a record of images, characters and/or the like, and has quickly spread as a recording system for recording apparatus of various images in various applications including information instruments because it has features such as recording can be conducted at high speed and with low noise, color images can be formed with ease, recording patterns are very flexible, and development and fixing processes are unnecessary. Further, it is beginning to be applied to a field of recording of full-color images because images formed by a multi-color ink-jet recording system are comparable in quality with multi-color prints by a plate making system and photoprints by a color photographic system, and such records can be obtained at lower cost than the usual multi-color prints and photoprints when the number of copies is small. With the improvement in recordability such as speeding up and high definition of recording and full-coloring of images, recording apparatuses and recording methods have been improved, and recording media have also been required to have higher properties. In order to satisfy such requirements, recording media have been variously improved so as to meet objects, applications and inks.
In the ink-jet recording system, droplets of an ink are ejected at high speed from a nozzle toward a recording medium. Since the ink contains a great amount of a solvent such as water or a mixed solvent of water and an organic solvent, a large amount of the ink is required to achieve a high color density. Since the ink droplets are continuously ejected, a beading phenomenon that the ink droplets fuse with each other, and dots of the ink aggregate, may occur after a first droplet is ejected, resulting in disorder of an image. Therefore, ink-jet recording media are required to combine great ink-absorbing capacity with high ink-absorbing speed.
Therefore, a great number of recording media, in which a porous layer comprising inorganic particles is formed, have been proposed. For example, in Japanese Patent Application Laid-Open No. 2-276670, a porous layer comprising an alumina hydrate is provided on a substrate for the purpose of enhancing absorbency, color reproducibility and resolution. Japanese Patent Application Laid-Open No. 4-101880 proposes a recording medium in which an ink-fixing layer is formed with a resin, which is transparent and dissolved in or swelled with a solvent contained in an ink, on a substrate.
In the ink-jet recording system, inks of the type that a dye component is dissolved in a solvent have heretofore been often used. However, in the case where a dye-based ink is used, the resulting print involves a problem that since the print is naturally poor in light fastness and ozone fastness, it undergoes fading or color change when it is stored for a long period of time. Therefore, Japanese Patent Application Laid-Open No. 58-136482 and U.S. Pat. No. 5,374,475 propose recording media in which a porous layer comprising a thermoplastic polymer material is provided on a substrate, and the porous layer is melted by the action of heat and pressure after printing to make the porous layer dense.
Japanese Patent Publication No. 2-31673 proposes a recording medium having an ink-receiving layer of a two-layer structure in which a layer of an inorganic pigment having a great ink-absorbing capacity is formed on a substrate, and an ink-receptive layer comprising an organic thermoplastic polymer is provided as the outermost layer.
On the other hand, pigment inks have been recently been increasingly used in place of the dye-based inks for the purpose of solving the problems of light fastness, water fastness and ozone fastness and providing images of higher optical density, and can also be applied to the ink-jet recording system.
In the case where a pigment ink is used, a problem that the resulting print becomes poor in rub-off resistance and water fastness when the image is exposed on the surface of a recording medium arises because a pigment contained in the ink is not dissolved in a solvent. Therefore, a mechanism that the pigment is captured and fixed is required. There is known a system that a polymeric fixing agent is contained in an ink in addition to a pigment component to fix the pigment by the polymeric fixing agent upon the impact of the ink. However, this system must be still improved to achieve high fixing ability. A recording liquid making combined use of a pigment and a dye is known from the viewpoint of providing images of high optical density.
Media suitable for pigment inks have been proposed in Japanese Patent Application Laid-Open Nos. 8-230308, 9-30116, 9-66660 and 9-123593.
However, the above-described prior arts have involved the following problem. Since a marked difference in particle and molecular sizes lies between pigments and dyes, mechanisms of fixing or adsorbing them differ greatly. Therefore, recording media suitable for use in dye-based inks are not always applicable to pigment inks. For example, when printing is conducted on the recording medium described in Japanese Patent Application Laid-Open No. 2-276670, portions, on which a pigment 200 and a dye 201 are deposited and exposed on the surface of the recording medium 302 as illustrated in FIG. 9, are formed when respective inks are ejected in great amounts, so that sufficient rub-off resistance and water fastness cannot be achieved in the resulting image. When printing is conducted on the recording medium described in Japanese Patent Application Laid-Open No. 4-101880, the viscosity and strength of the resin portion are continuously reduced due to the dissolution or swelling of the resin portion in or with a solvent in an ink, and ink-absorbing speed is slowed, so that its sticking and separation by contact occur. In addition, the color density of the resulting image is also insufficient. When printing is conducted on the recording medium described in Japanese Patent Application Laid-Open No. 58-136482 or U.S. Pat. No. 5,374,475, coloring materials, both pigment component and dye component, are trapped in a microporous layer through a microporous structure. Therefore, the pigment component 200 large in particle diameter is dispersed and arranged by halves in pores in the resin layer 402 as illustrated in FIG. 10, so that the optical density of the resulting image cannot be enhanced even when the amount of the ink is increased.
The recording medium described in Japanese Patent Publication No. 2-31673 is designed so as to achieve a more sufficient ink-absorbing capacity, but not intended to be applicable to pigment inks as well. More specifically, since correlation between a pigment and the size of pores in the resin layer is not optimized, the pigment component in the pigment ink is dispersed and arranged in pores in the resin layer provided on the inorganic pigment layer, so that the optical density of the resulting image cannot be enhanced even when the amount of the ink is increased.
Some problems are involved in the above-described media suited to pigment inks as well.
In Japanese Patent Application Laid-Open No. 8-230308, a porous undercoat layer having a pore size of the submicron order is provided on a substrate, and an overcoat layer containing plastic beads and having pores of the micron order is provided thereon to trap a pigment forming an image in the pores of the micron order in the overcoat layer. However, since the pigment trapped is dispersed in a vertical direction of the overcoat layer to penetrate thereinto, it is difficult to realize a high optical density of image. In addition, since the pigment only penetrates into the pores in the overcoat layer, and is not fixed, the recording medium has a problem that the resulting print is lacking in long-term reliability upon its storage.
In Japanese Patent Application Laid-Open No. 9-30116, a surface layer 603 having pores through which a pigment 200 passes, and an ink-holding layer 602 are provided on a transparent substrate 601 as illustrated in FIG. 11. In this medium, the pore volume and pH of the surface layer are adjusted so as to conduct printing with a pigment ink from the side of the surface layer 603, and an image formed is observed from the side of the transparent substrate 601. However, the medium involves a problem that when characters are printed, an apparatus for printing reflected-image characters and a pretreatment of the image are required. In addition, since the surface layer 603 has the pores of the size that the pigment can pass through, the transparency of the surface layer 603 is lowered, and so the medium has been not suitable for a recording medium of the transmission type such as OHP.
In Japanese Patent Application Laid-Open No. 9-66660, a porous alumina hydrate layer is provided as a lower layer on a substrate, and another porous layer having a smaller average pore diameter than the porous alumina hydrate layer is provided thereon. In this medium, the upper layer controls an ink-absorbing speed to uniformly disperse and absorb a pigment ink. However, the ink-absorbing speed of the upper layer is slow, and so problems such as feathering have arisen when a large amount of the ink is ejected.
In Japanese Patent Application Laid-Open No. 9-123593, a porous alumina hydrate layer having a thickness of 1 to 200 xcexcm is provided on a substrate, and a water-soluble resin layer having a thickness of 0.01 to 50 xcexcm is provided thereon to absorb a solvent in an ink and swell, thereby moderately controlling a drying speed. However, this medium has problems that the medium takes a long time from the swelling to the drying, and that feathering occurs when a large amount of the ink is ejected.
With the foregoing problems in view, it is an object of the present invention to provide an ink-jet recording method, by which even when a pigment ink comprising a pigment component as a coloring material is used, the pigment can be uniformly fixed to achieve a high optical density of image, and a print obtained by such an ink-jet recording method.
The above object can be achieved by the present invention described below.
According to the present invention, there is thus provided an ink-jet recording method in which recording is conducted with an ink comprising a pigment component on a recording medium comprising a substrate and a porous layer including polymer particles provided thereon, the method comprising,
in the case where the pore diameter distribution of the porous layer including polymer particles and the particle diameter distribution of the pigment component are both expressed in terms of frequency distribution, controlling a proportion of the frequency of the pore diameter of the porous layer including polymer particles, which overlaps the particle diameter distribution of the pigment component, to the frequency of the whole pore diameter of the porous layer including polymer particles to from 0.1% to 10% to form an image; and
heat-treating the porous layer including polymer particles after the formation of the image.
According to the present invention, there is also provided a print on a recording medium comprising a substrate and a polymer resin layer provided on the substrate, wherein a pigment component in an ink is fixed in the vicinity of the surface of the polymer resin layer, and a dye component in the ink is fixed on the substrate.
According to the present invention, there is further provided a print on a recording medium comprising a substrate, a porous layer including inorganic pigment and a polymer resin layer successively formed on the substrate, wherein a pigment component in an ink is fixed in the vicinity of the surface of the polymer resin layer, and a dye component in the ink is fixed into the porous layer including inorganic pigment.